New estimates from Columbia University show that if the U.S. had imposed social distancing one week earlier than it did in March, about 36,000 fewer people would have died from COVID-19. The New York Times writes an even earlier lockdown would have saved thousands more:

And if the country had begun locking down cities and limiting social contact on March 1, two weeks earlier than most people started staying home, the vast majority of the nation’s deaths — about 83 percent — would have been avoided, the researchers estimated. Under that scenario, about 54,000 fewer people would have died by early May.

As state reopen, the data shows just how quickly the virus can flare up, spread and get out of control.

The Times points to a tweet by Donald Trump on March 9 that said in part, “Nothing is shut down, life & the economy go on.”

In fact, tens of thousands of people had already been infected by that point, researchers later estimated. But a lack of widespread testing allowed those infections to go undetected, hiding the urgency of an outbreak that most Americans still identified as a foreign threat.